Autophagy regulates myeloid cell differentiation by p62/SQSTM1-mediated degradation of PML-RARα oncoprotein

p62/SQSTM1 upregulation constitutes a survival mechanism that occurs during granulocytic differentiation of acute myeloid leukemia cells

“…p62/SQSTM1 upregulation was also shown during maturation of AML cells into either monocytes (Figure 1e) or megakaryocytes (data not shown). 23 Of note, our findings differ from those reported by Wang et al 49 who showed that p62/SQSTM1 is downregulated upon ATRA treatment of AML cells and contributes to their differentiation. To explain this discrepancy, we compared the expression of p62/SQSTM1 following cell lysis in two different lysis buffers and by using two different antibodies against p62/SQSTM1 (detailed information in Materials and Methods).…”

“…Along this line, autophagy has been shown to contribute to the degradation of PML-RARa, a leukemogenic protein, through a mechanism that involved the binding of p62/SQSTM1 to PML-RARa. 48,49 Yet, how PML-RARa is recognized and directed to autophagosomes by p62/SQSTM1 is not elucidated. Interestingly, PML-RARa is, in turn, involved in the activation of constitutive autophagy activity implying a mutual regulation between PML-RARa and autophagy pathways.…”

“…Fractions (30 mg to 50 mg) of cellular extract were subjected to SDS-polyacrylamide gel electrophoresis using a Tris/glycine buffer system based on the method of Laemmli as previously described. 56 'The p62/SQSTM1 protein levels were assessed following immunoblot analysis by using two different anti-p62/SQSTM1 antibodies: one from (BD Transduction Laboratory, #610832) and one from Santa Cruz biotechnology (#SC28359), which was used by Wang et al 49 Determination of aggregated proteins. Expression of aggregated proteins was determined by (i) immunoblot analysis of Triton X-100 using an antibody against polyubiquitinated proteins (ii) immunofluorescence analysis of polyubiquitinated proteins in cells , and (iii) measurement of aggresome formation using the ProteoStat Aggresome detection kit.…”

Role of autophagy in the progression and suppression of leukemias

“…A recent report indicated that the Akt inhibitor triciribine increased apoptosis in T-cell ALL by a process in which autophagy played a defensive role as shown by increased apoptosis when autophagy was inhibited [107]. Similarly, suppression of autophagy with shRNAs and specific inhibitors resulted in blocking of PML-RAR␣ oncoprotein degradation and granulocytic differentiation in myeloid leukemia cells [108]. CML cells expressing BCR/ABL oncoprotein at high levels were shown to induce autophagy in order to recover from targeted and nontargeted treatment options, indicating the protective effect of autophagy in CML [109].…”

Genomic instability establishes dependencies on acquired gene regulatory networks: A novel role of p62 in myeloid malignancies with del(5q)

“…An essential role of p62 in TRAF6/NF-kB activation has been described in solid tumors, 8 and also recently in the survival of AML cells during all-trans retinoic acidinduced differentiation. 9 Given that concomitant loss of miR-146a and overexpression of p62 cooperate to enhance TRAF6/NF-kB signaling by derepressing and activating TRAF6, respectively, we hypothesize that del(5q) MDS/AML cells are vulnerable to disruption of the p62-TRAF6 complex. As expected, knocking down p62 or disrupting p62-TRAF6 binding results in cell cycle arrest and apoptosis in MDS/AML cell lines and patient samples.…”